calc - Calculate date/time differences

Calculate the difference between two dates or times using natural language expressions.

For Claude Code

If you are Claude: DO NOT invoke this slash command. Use unix timestamp arithmetic via Bash tool:

date1=$(date -d "first date" +%s)
date2=$(date -d "second date" +%s)
diff=$((date2 - date1))
echo "Difference: $diff seconds"

See the Implementation section below for the full calculation pattern.

For Users

Usage

/datetime:calc

The command will interactively ask for two date/time expressions, then calculate the difference.

What it does

1. Asks for first date/time: Accepts natural language expression (e.g., "tomorrow", "2024-12-01", "next Monday")
2. Asks for second date/time: Accepts natural language expression
3. Calculates difference: Shows the time between the two dates in multiple units
4. Human-readable output: Displays results as days, hours, minutes, and seconds

The calculation uses unix timestamps internally for accuracy across timezones and DST boundaries.

Implementation

Convert dates to unix timestamps:

date1_ts=$(date -d "first expression" +%s)
date2_ts=$(date -d "second expression" +%s)

Calculate difference:

diff_seconds=$((date2_ts - date1_ts))
diff_days=$((diff_seconds / 86400))
diff_hours=$(((diff_seconds % 86400) / 3600))
diff_minutes=$(((diff_seconds % 3600) / 60))
diff_secs=$((diff_seconds % 60))

Display result:

echo "Difference: ${diff_days}d ${diff_hours}h ${diff_minutes}m ${diff_secs}s"
echo "Total: ${diff_seconds} seconds"

Examples

# Days until deadline
/datetime:calc
→ First date/time: today
→ Second date/time: 2024-12-15
→ Difference: 32d 0h 0m 0s (32 days)
→ Total: 2764800 seconds

# Time since event
/datetime:calc
→ First date/time: 2024-11-01
→ Second date/time: today
→ Difference: 12d 0h 0m 0s (12 days)
→ Total: 1036800 seconds

# Hours between meetings
/datetime:calc
→ First date/time: today 14:00
→ Second date/time: tomorrow 10:30
→ Difference: 0d 20h 30m 0s
→ Total: 73800 seconds

# Working days remaining
/datetime:calc
→ First date/time: today
→ Second date/time: next Friday
→ Difference: 2d 0h 0m 0s (2 days)
→ Total: 172800 seconds

Common calculations

Academic deadlines:

• "today" to "2024-12-20" - Days until assignment due
• "today" to "next Friday 23:59" - Time to weekly submission

Project milestones:

• "2024-11-13" to "2024-12-01" - Sprint duration
• "last Monday" to "today" - Week progress

Event planning:

• "today" to "25 Dec" - Days until event
• "9:00" to "17:00" - Meeting duration (same day)

Time tracking:

• "yesterday" to "today" - Daily intervals
• "1 week ago" to "today" - Weekly reviews

When to use

• Calculate days remaining until assignment deadlines
• Track time elapsed on projects or sprints
• Plan event schedules and milestones
• Verify working time between meetings
• Calculate age or duration of events
• Estimate remaining time for deliverables
• Academic semester/week planning

Related commands

• /datetime:now - Get current date/time
• /datetime:parse - Parse natural language date expressions